The present invention is directed to a bicycle crank axle, a crank arm, and a crank set that offer high mounting precision and fastening strength, and that contribute to lighter weight. It also relates to a bolt and assembly tools used for assembling these components.
In conventional mounting mechanisms for the crank arms and crank axle in a bicycle, both ends of the crank axle are shaped into essentially square columns, a square hole is made in each crank arm, and the two are fitted together to fasten the crank arm onto the axle. The precision of centering afforded by the conventional mechanism for fitting together the crank arms and the crank axle is inadequate, and the strength of the linkage in the direction of rotation is inadequate as well. The problem of inadequate linkage strength is particularly notable where an aluminum alloy hollow pipe structure has been adopted for the crank axle, or where an aluminum alloy hollow structure has been adopted for the crank arms in order to reduce weight.
The present invention is directed to a bicycle crank axle, a crank arm, and a crank set that offer high mounting precision and fastening strength, but also contribute to lighter weight. Novel bolt and assembly tools used are for installing and removing these components so that assembly and disassembly may be accomplished very easily.
In one embodiment of the present invention, a crank axle includes an axle body having first and second ends, a first rotary linkage member disposed at the first end of the axle body for nonrotatably fitting a first crank arm thereto, and a first centering structure disposed at the first end of the axle body in close proximity to the first rotary linkage member. If desired, the rotary linkage member may be formed as a plurality of splines, and the same structure may be formed at the second end. A crank arm for fitting to the crank axle includes a crank axle mounting section having a centering structure for centering the crank axle mounting section to an end of a crank axle, and a rotary linkage member for nonrotatably fitting the crank axle mounting section to the end of the crank axle. If desired, the rotary linkage member for the crank arm may comprise splines that mesh with splines on the end of the crank axle. Such a structure provides secure linking of the crank arm to the crank axle without adding excessive weight.
To facilitate removal of the crank arm, a special bolt is used to fix the crank arm to the crank axle. The bolt includes a head, a threaded section having a diameter greater than or equal to the head, and a flange disposed between the head and the threaded section. The flange preferably has a diameter greater than the diameter of the threaded section, and the head defines a multiple-sided tool-engaging hole which extends axially into the threaded section to maximize the tool engaging surface. The crank axle mounting section of the crank arm preferably includes a stop ring or similar structure located so that the flange of the bolt is disposed between the stop ring and the first end of the axle body. As a result, the bolt flange presses the crank arm apart from the crank axle when the bolt is loosened.
Special tools may be provided to allow easy installation and removal of the components. For example, a tool that can be used for both fixing the axle to the bicycle and fixing a chainwheel to the crank arm includes a tool-mount member shaped to be held and turned by a tool, wherein the tool-mount member defines an opening for receiving a portion of the axle body therethrough. An operating member having a plurality of splines formed on an inside surface thereof is coupled to the tool-mount member. The splines may engage corresponding splines on a mounting adapter for the crank axle or corresponding splines on a nut used to fix a chainwheel to the crank arm. In the latter case, an auxiliary tool may be provided to ensure stable operation of the tool. The auxiliary tool may include a grip section disposed in close proximity to a first end thereof, wherein the grip section has a diameter greater than or equal to a diameter of an end of the crank axle. A support section may be disposed adjacent to the grip section and sized to fit within the opening in the tool-mount member. A second end of the auxiliary tool has a threaded inner peripheral surface which can engage with the bolt used to mount the crank arm to the axle. In this case the bolt serves to temporarily fix the main and auxiliary tool to the crank arm so that the main tool can reliably tighten the chainring fixing nut.